From: Peter Zijlstra <peterz@infradead.org>
To: mingo@kernel.org, linux-kernel@vger.kernel.org
Cc: subhra.mazumdar@oracle.com, steven.sistare@oracle.com,
dhaval.giani@oracle.com, rohit.k.jain@oracle.com,
umgwanakikbuti@gmail.com, matt@codeblueprint.co.uk,
riel@surriel.com, peterz@infradead.org
Subject: [RFC 01/11] sched/fair: Fix select_idle_cpu()s cost accounting
Date: Wed, 30 May 2018 16:22:37 +0200 [thread overview]
Message-ID: <20180530143105.926359095@infradead.org> (raw)
In-Reply-To: 20180530142236.667774973@infradead.org
[-- Attachment #1: peterz-sis-again-1.patch --]
[-- Type: text/plain, Size: 1423 bytes --]
We compute the average cost of the total scan, but then use it as a
per-cpu scan cost when computing the scan proportion. Fix this by
properly computing a per-cpu scan cost.
This also fixes a bug where we would terminate early (!--nr, case) and
not account that cost at all.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
kernel/sched/fair.c | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6368,11 +6368,11 @@ static inline int select_idle_smt(struct
*/
static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int target)
{
+ int cpu, loops = 0, nr = INT_MAX;
struct sched_domain *this_sd;
u64 avg_cost, avg_idle;
u64 time, cost;
s64 delta;
- int cpu, nr = INT_MAX;
this_sd = rcu_dereference(*this_cpu_ptr(&sd_llc));
if (!this_sd)
@@ -6399,8 +6399,10 @@ static int select_idle_cpu(struct task_s
time = local_clock();
for_each_cpu_wrap(cpu, sched_domain_span(sd), target) {
- if (!--nr)
- return -1;
+ if (loops++ >= nr) {
+ cpu = -1;
+ break;
+ }
if (!cpumask_test_cpu(cpu, &p->cpus_allowed))
continue;
if (available_idle_cpu(cpu))
@@ -6408,6 +6410,7 @@ static int select_idle_cpu(struct task_s
}
time = local_clock() - time;
+ time = div_u64(time, loops);
cost = this_sd->avg_scan_cost;
delta = (s64)(time - cost) / 8;
this_sd->avg_scan_cost += delta;
next prev parent reply other threads:[~2018-05-30 14:37 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-05-30 14:22 [RFC 00/11] select_idle_sibling rework Peter Zijlstra
2018-05-30 14:22 ` Peter Zijlstra [this message]
2018-05-30 14:22 ` [RFC 02/11] sched/fair: Age the average idle time Peter Zijlstra
2018-05-30 14:22 ` [RFC 03/11] sched/fair: Only use time once Peter Zijlstra
2018-05-30 14:22 ` [RFC 04/11] sched/topology: Introduce sched_domain_cores() Peter Zijlstra
2018-05-30 14:22 ` [RFC 05/11] sched/fair: Re-arrange select_idle_cpu() Peter Zijlstra
2018-05-30 14:22 ` [RFC 06/11] sched/fair: Make select_idle_cpu() proportional to cores Peter Zijlstra
2018-05-30 14:22 ` [RFC 07/11] sched/fair: Fold the select_idle_sibling() scans Peter Zijlstra
2018-05-30 14:22 ` [RFC 08/11] sched/fair: Optimize SIS_FOLD Peter Zijlstra
2018-05-30 14:22 ` [RFC 09/11] sched/fair: Remove SIS_AVG_PROP Peter Zijlstra
2018-05-30 14:22 ` [RFC 10/11] sched/fair: Remove SIS_AGE/SIS_ONCE Peter Zijlstra
2018-05-30 14:22 ` [RFC 11/11] sched/fair: Remove SIS_FOLD Peter Zijlstra
2018-06-19 22:06 ` [RFC 00/11] select_idle_sibling rework Matt Fleming
2018-06-20 22:20 ` Steven Sistare
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20180530143105.926359095@infradead.org \
--to=peterz@infradead.org \
--cc=dhaval.giani@oracle.com \
--cc=linux-kernel@vger.kernel.org \
--cc=matt@codeblueprint.co.uk \
--cc=mingo@kernel.org \
--cc=riel@surriel.com \
--cc=rohit.k.jain@oracle.com \
--cc=steven.sistare@oracle.com \
--cc=subhra.mazumdar@oracle.com \
--cc=umgwanakikbuti@gmail.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).